function init(){
	
	window.onscroll = function(){
		
		var  Yheight = document.body.scrollTop || document.documentElement.scrollTop;
		
		var h = 500;
		var opacity =0;
		if(Yheight>h){
			
			opacity = 1;
			
		}else{
			opacity = Yheight/h*1;
			console.log(opacity);
			
		}
		
		$('#nav_header .navbar').css('background-color','rgba(231,231,231,'+opacity+')');
	}
	
	
	
	
}

init();
